The invention relates to an arrangement in a planetary gearing where the arrangement includes:                A planet gear including at least three planet wheels each of which has an inner race supported by at least one bearing and further a shaft supporting this bearing,        A planet carrier including a first flange connected to an input shaft and a second flange on the opposite side, andeach planet wheel shaft has        A first end non-rotatably adapted to said first flange over a first support length,        A center area thicker than the first end for supporting the bearing,        A second end non-rotatably adapted to said second flange over a second support length, and the arrangement further includes a construction allowing flexing in each shaft for dynamically adapting the mesh geometry of several planet wheels to the elasticity of the construction. The invention also relates to a planetary gear driving the arrangement.        
The most essential parts of the planetary gear are a sun wheel, a gear rim, and a planet gear between these. The gear rim also refers to a gear rim assembly that is composed of components connected to each other. The planet gear including at least three planet wheels is concentric with the sun wheel and the gear rim. The planet wheels are mounted with bearings to a planet carrier, which includes a first flange and a second flange tied to each other. The power input shaft is connected to the planet carrier, more precisely to its first flange, i.e. it carries the maximum torque. The sun wheel or the gear rim can be locked, in which case two of the others, the sun wheel, gear rim or carrier, rotate about the center axis of the sun wheel.
Each planet wheel has a shaft that is firmly tied to the carrier by both of its ends. The planet wheel is adapted to rotate about the shaft by means of at least one bearing, usually with two bearings.
The shaft flexes relative to the construction allowing flexing which is located in connection with the first end for dynamically adapting the mesh geometry. In this publication the term ‘dynamic adaptation’ is used to refer to that the load of the planet wheels is balanced regardless of various manufacturing inaccuracies and shaft deformations due to the load. When a flexible or an elastic shaft adapts the mesh geometry dynamically, larger deformations than before can be allowed for the carrier. In other words, the shaft is used to compensate misalignments caused by the torsion of the carrier.
Publication WO 2006/053940 discloses a planetary gear of a wind power plant. In such planetary gears, setting has been generally improved by correcting the tooth profile. The tooth profile can be corrected with helix angle modification, crowning and/or end relief. However, a problem with the tooth profile correction is that it must be accurately dimensioned to a certain relatively narrow output range. In a wind power plant, the planetary gear should operate in a wide output range. However, this cannot be achieved by correcting the tooth profile.
In turn, patent application WO 2005/038296 discloses equipment in which the planet wheel shaft is dimensioned to deflect. A deflecting shaft can make the planet wheels set better in the planetary gear. Setting is necessary since planetary gear components always have slight inaccuracy.
The solutions proposed in patent publications WO 2007/016336 and GB 2413836 for the dynamic adaptation of the mesh geometry are also based on the deflection of a long shaft. With these, the mesh geometry of several planet wheels sets in place for each planet wheel when their shafts flex suitably correcting the effect of manufacturing inaccuracy.
Publication DE 102004023151 proposes a planetary gear that has a flange in connection with the shaft. This construction helps compensate manufacturing defects, for example. However, these solutions do not provide a remarkable benefit from relieving of the carrier since the combined size of the shaft and the flange increases remarkably. In a version equipped with a flange, a great part of the benefit achieved by relieving the carrier is thus lost.
Closest to the invention are the solutions proposed in patent publications EP 1435475 and U.S. Pat. No. 5,102,379 where a double-flanged carrier is used to support the planet wheel shafts at both ends. In these, the deflecting length of the shaft is formed within the thicker center part as a deep axial cavity has been machined in the center part. The EP publication discloses additionally the asymmetric construction of the shaft, which is necessary for providing a perfect dynamic adaptation. In the speed-reducing planetary gear of the EP publication, torque is conveyed to the sun wheel whereby the torque acting on the first flange of the carrier is proportionally much lower than in a planetary gearing that increases the rotation speed. The notch effect of the circumferential cavity is not significant due to the lowness of the torque.
The above known solutions are suitable mainly to planetary gearings that reduce rotation speed. Known solutions are difficult to use in heavy wind turbine applications in which the torque is today in a range of 1-10 millions Nm. In jet engine motors the maximum torque is only a fraction of this since the rotation speed of a turbine is 3000-6000 RPM and in a speed-reducing planetary gearing the force is conveyed to the sun wheel whereby the carrier's torque remains naturally low. Planetary gears of wind turbines are today very large and they are used to transmit high output powers from a slowly rotating rotor. Thus planetary gears used in wind turbines have many special features. One significant special feature is that they are used to increase the rotation speed while planetary gears are typically used elsewhere to reduce the rotation speed. In addition, the size of the planetary gear is very essential because it is desired to limit the mass lifted up to a mast. However, it is difficult to reduce the size of a high-output planetary gear because all the methods of the conventional machine design have already been used.
As regards the size reduction of a planetary gear, it would be advantageous to increase the number of planet wheels but, according to prior art, it is necessary to increase dimensional loads when the number of planet wheels goes up from three, due to the assumed uneven load (Germanischer Lloyd, Guideline for the Certification of Wind Turbines, Edition 2003). As dimensional loads increase, a major part of the benefits achieved while increasing the number of planet wheels up from three with conventional methods is typically lost.